Immunohistochemical analysis of thymidylate synthase, p16^INK4a, cyclin‐dependent kinase 4 and cyclin D1 in colorectal cancers receiving preoperative chemotherapy: Significance of p16^INK4a‐mediated cellular arrest as an indicator of chemosensitivity to 5‐fluorouracil

Abstract

High expression of thymidylate synthase (TS) is allegedly associated with the chemoresistance to 5-fluorouracil (5-FU) in colorectal cancers. However, low TS expression does not necessarily imply chemosensitivity. Inactivation of p16(INK4a) correlates with poor prognosis in various cancers. We immunohistochemically evaluated the relationship between the expression of TS, p16(INK4a), CDK4 and cyclin D1 and the effect of 5-FU-based chemotherapy in colorectal cancers. After antigen retrieval, immunoperoxidase staining was performed on the paraffin-embedded, biopsy and surgical specimens of 37 advanced colorectal cancers preoperatively treated with peroral administration of 5-FU derivatives. As a control group, 31 colorectal cancers without preoperative treatment were analyzed. High TS expression was found in 23 (74%) of 31 tumors resected from histological non-responders and in 19 (61%) of 31 controls but in none of six responders. High p16(INK4a) expression was seen in 83% of the responders, 52% of the non-responders and 32% of the controls. The TS-low/p16(INK4a)-high phenotype was noted in 83% of the responders, but only in 3% of the non-responders (P = 0.0001). Induction of p16(INK4a) expression after chemotherapy was predominantly seen in the responders. Neither CDK4 nor cyclin D1 expression was related to the chemotherapeutic effects. In conclusion, the combination of low expression of TS and induction of p16(INK4a) after chemotherapy can be important indicators of the sensitivity to 5-FU-based chemotherapy in colorectal cancers.

Expression of thymidylate synthase in human cells is an early G1 event regulated by CDK4 and p16INK4A but not E2F

“…As shown in this report, TS expression is decreased both by small molecule inhibitors of CDK4 and following over-expression of p16INK4A. Interestingly, it has been previously shown that tumour tissue from patients who responded to fluoropyrimidine-based treatment expressed high levels p16INK4A (Kamoshida et al, 2004). Since we have shown that CDK4 regulates TS expression, high levels of p16INK4A would be expected to decrease TS levels and to sensitise cells to anti-TS drugs.…”

Expression of p16 in lymph node metastases of adjuvantly treated stage III colorectal cancer patients identifies poor prognostic subgroups

“…resection specimens and observed significant overexpression of p16 in resection specimens from patients who had a response to 5-FU-based chemotherapy compared with nonresponders and controls. 54 Our major novel findings suggest that negative p16 expression evaluated in lymph nodes, rather than in primary tumors, from patients with stage III disease who received adjuvant therapy is a highly adverse prognostic indicator. In fact, negative p16 expression was related to worse survival in both pT3 and pT4 disease and was independent of patient age, LNR, performance status, treatment with folic acid, and chemotherapy regimen.…”

Pharmacokinetics, Metabolism, and Oral Bioavailability of the DNA Methyltransferase Inhibitor 5-Fluoro-2′-Deoxycytidine in Mice

“…However, whereas FdUrd and the other downstream metabolites of FdCyd are incapable of inhibiting DNA methyltransferase, they do have potent cytotoxic activity, and 5-FU and FdUrd are frequently used therapeutically (32,33). In addition, their cellular effects result in cell cycle arrest, which inherently prevents incorporation of FdCyd into DNA (34). There still exists the possibility of metabolite formation via deoxycytidylate deaminase (dCMP deaminase; Fig.…”